1. Field of the Invention
The present invention relates to a projection display device, which separates white light from a light source into three-color lights of red, blue and green, modulates these color lights through a light valve composed of a liquid crystal panel or the like in response to image information, and recombines the modulated lights with an optical combining means to enlarge and project an image onto a projecting surface through a projection means.
2. Description of Related Art
A mechanism for fixing a light valve onto a prism body which is an optical combining means for a projection display device is disclosed in Japanese Patent Laid-Open Publication No. Hei 6-118368. In this fixing mechanism, the light valve is directly fixed onto the light incident face of the prism body with an adhesive.
The use of such a mechanism permits the omission of a pixel alignment mechanism between a plurality of light valves, which modulate the light which is particularly separated into red, green and blue, and a focussing mechanism, which adjusts the position of the formation face of each image which becomes an object within the focal depth of a projection lens. Accordingly, miniaturization and weight reduction of the optical system and reduction of the number of parts can be achieved in a projection display device.
However, when the light valve is directly bonded and fixed to the light incident surface of the prism body, it involves the following problems to be solved.
First, external light which enters from the external part of the device enters the light valve, there may be a possibility that each element may be operated by mistake. Moreover, direct handling of the light valve may cause its breakage, and this is not desirable. For example, direct chucking of the light valve, for bonding the light valve by a jig to the prism body may cause breakage at the edge, corner or the like of the light valve. Further, because the light valve is easily affected by static electricity, direct contact of the light valve for bonding it to the prism body is not desired.
In the light valve bonded to the prism body, part of the pixels may develop defects or the like as time passes by and the light valve changes. A light valve having defects must be replaced with a new one. However, it is difficult to exchange the light valve with defects with a new one since it is bonded and fixed to the prism body. It is not easy to detach the bonded and fixed light valve without damaging the light incident face of the prism body. Because of this, there are cases, for example, when exchanging the light valve with defects including the prism body, and this is not economical.
Furthermore, when the light valve is directly bonded and fixed to the prism body, the linear expansion coefficient of the light valve and the prism body are difficult so that thermal distortion may occur.
It is an object of the present invention to provide a projection display device having a fixing mechanism of a light valve, in which the light valve can be readily detached and is not easily affected by thermal distortion.
In order to solve the above-mentioned problems, in the present invention, a projection display device which separates light from a light source into a plurality of color lights, modulates each color light through a light valve in response to image information, and recombines the modulated lights of each color with an optical combining means comprising a prism body to enlarge and project an image onto a screen through a projection means, wherein the structures are used such that the periphery of the light valve is protected to prevent the invasion of external light, breakage and the like, and the light valve is detachably fixed on the prism body.
That is, the present invention includes a fixing frame plate fixed onto the light incident face of the prism body with an adhesive, a light valve frame plate for holding the light valve, a fixing means for detachably fixing the light valve frame plate onto the fixing frame plate, and a positioning means for positioning the light valve for the light incident face of the prism body. The fixing frame plate is formed by a material having a linear expansion coefficient ranging from xc2xc to 4 times and preferably from xc2xd to 2 times the linear expansion coefficient of the prism body, and the light valve frame plate is formed by a material where the linear expansion coefficient ranges from ⅕ to 5 times, preferably from xc2xd to 2 times.
In the projection display device of the present invention having such a configuration, the light valve is held by the light valve frame plate. Furthermore, on the light incident face of the prism body, the fixing frame plate is attached and fixed, and on this fixing frame plate, the light valve frame plate in which the light valve is held is detachably fixed.
Accordingly, since the light valve frame plate protects the periphery of the light valve, the light valve will not break when fixing it onto the prism body or the like. Further, in a state where the light valve is built in the projection display device, because the periphery is covered by a light valve frame plate, there is no possibility that there may be an operation by mistake because of the entrance of the external light.
Furthermore, when some defects occur in the light valve as time passes by and the light valve changes, the light valve frame plate which holds the light valve can be detached from the fixing frame plate, which is bonded and fixed to the prism body, and it is good to fix the light valve frame plate which holds the new light valve to the fixing frame plate. Thus, since the light valve is not directly bonded and fixed to the prism body, the light valve can be easily replaced without damage to the front surface of the prism body.
When the fixing frame plate and the light valve frame plate have specified ranges of linear expansion coefficients compared to that of the prism body, distortion of these members by thermal expansion will not adversely affect focusing adjustment and alignment adjustment. Furthermore, if the prism body, fixing frame plate, and light valve frame plate define the linear expansion coefficient as E1, E2, and E3, respectively, it is most preferable that the linear expansion coefficient E1, E2, and E3 is the same, but at least, it is preferable that the relationship of E1 less than E2 less than E3 is established. By having a linear expansion coefficient, which is larger than that of the prism body and smaller than that of the light valve frame plate, the linear expansion coefficient of the fixing frame plate is positioned between the prism body composed of optical glass having a small linear expansion coefficient and the light valve frame plate formed by a material generally having a larger linear expansion coefficient, the effect of thermal distortion caused by the difference in linear expansion coefficient among the three things can be moderated.
The projection display device may further include a medial frame plate provided between the fixing frame plate and the light valve frame plate, the medial frame plate is fixed to the fixing frame plate by the fixing means, and is bonded and fixed to the light valve frame plate in a state positioned by the positioning means.
When the medial frame plate is provided, a temporary fixing means is provided between the medial frame plate and the light valve frame plate to temporarily fix the medial frame plate and the light valve frame plate. After temporarily fixing the medial frame plate and the light valve frame plate, these frame plates are then positioned by the positioning means, and the positioning means is preferably bonded and fixed.
The light valve frame plate has a first frame plate and a second frame plate, and can use the structure which can hold in a state where the light valve is inserted between these frame plates.
A plurality of wedge members can be used as the positioning means. The positioning means is used for adjusting the bonding and fixing position of the fixing frame plate which is fixed on the light incident face of the prism body and the fixing position of the light valve to the fixing frame. In general, the wedge members may be bonded and fixed to the respective members after the member positioning is completed.
A liquid crystal device can be used as the light valve. The present invention is particularly effective for a liquid crystal device which has inferior electrostatic resistance and can easily cause an erroneous operation due to the invasion of external light.
As the light valve, a light transmission type or a light reflection type exists. Generally, in the light reflection type of light valve, the color combining means also functions as a light separating means for separating light from the light source into a plurality of color lights.
As a projection display device, two kinds of devices exist: a front-surface projection display device which projects the projecting surface from the observing side and a rear-surface projection display device which projects the projecting surface from the opposite direction of the observing side. The present invention is applicable to either type of device.
When a dichroic prism is used as the prism body, the light valve is positioned and fixed onto the face of the dichroic prism using the fixing frame plate, light valve frame plate, fixing means, and the positioning means. It is considered that this fixing structure can be applied to a structure where a solid-state imaging element of a CCD or the like is positioned and fixed to the color separating prism in a camera or the like.